All wheel drive vacuum solenoid and hose diagram for 91 Caravan

[Force Fed Mopar]

Does anyone have this? trying to find out why mine isn't putting any power to the rear wheels.

[moparman76_69]

I have a good portion of the AWD parts of the FSM scanned as PDFs if you want to PM me your email and I'll send them to you.

[Force Fed Mopar]

You, sir, are the man! PM sent.

[Reaper1]

I hope the VC is OK. From what I gather that's probably the most likely failure point beyond the PTU if the previous owner/s didn't service it and the gears went *poof* due to lack of good fluid. I *thought* I remember seeing an aftermarket supplier for the PTU gears at some point.

[c2xejk]

A bit of a hijack here, but I have been wondering what is meant by "overrunning" and "locked-up"?

In "overrunning" is it possible to do a burnout with the front wheels and not send power to the rear wheels? Then switch to "locked-up" for a launch?

Thanks

[Reaper1]

In a word, no. The overrunning bearing (or sprag as some people know it) is there to allow the rear tires to turn faster than the fronts (like if you locked the front tires trying to stop, etc.). The dog clutch is there for reverse...so you have AWD in reverse. There's speculation about what would happen if you actuated the dog clutch in forward. In all honesty I don't know that it would truly make that big of a difference simply because of the way the entire system works. If the overrunning bearing is locked (which should be ANY time the fronts are spinning fast enough to actuate the VC in forward), the dog clutch being locked only increases the mechanical transfer of the torque and spreads that load over more elements.

The gearing from the front differential, PTU and the rear axle are slightly different on purpose. It is done in such a way that the front is always being driven slightly faster than the rear (if I remember the ratios correctly). What this does is introduce a very small amount of slippage in the VC. It's about 1-2%. What this does is allow for *immediate* transfer of torque to the rear when it's needed due to the way the VC works. The VC is NEVER 100% locked unless it's broken. I swear I remember reading an article someplace that said the VC can transfer something along the lines of 90% of the torque to the rear.

http://www.allpar.com/eek/awd.html